1. The invention relates to an image guided surgery system, comprising a position measuring system which includes a detector arrangement and a marker arrangement.
2. Description of Related Art
A system of this kind is described in WO-A1-97/40763. Two cameras, capable of detecting visible light or infrared light, are mounted on a stand so as to be immobile in space. An instrument for treatment is provided with diodes which emit light that can be detected by the cameras. Using the cameras, the position of the instrument can be determined in a co-ordinate system coupled to the cameras. This position can be converted into an image position by means of a predetermined transformation matrix, the image having been acquired in advance, for example by means of computer tomography (CT) or magnetic resonance tomography (MR). In order to determine said transformation matrix for converting camera co-ordinates into image co-ordinates, markers are provided on the patient during the image acquisition, said markers also being reproduced so as to be visible in the image. Subsequently, the markers are approached by the instrument provided with diodes or by a separate indicator instrument provided with diodes, so that the position thereof is detected in camera co-ordinates. The necessary link between camera co-ordinates and image co-ordinates is thus established and the position of the instrument during a treatment can be indicated in the image.
A position measuring system of this kind is preferably used in neurosurgery so as to show the surgeon the current position of the instrument in the brain of the patient being treated in the image. However, it is a drawback of the known system that the direct line of sight between the detector arrangement (the cameras) and the marker arrangement (the LEDs) may not be blocked, for example by attending staff or other apparatus, in order to ensure continuous and correct operation of the position measuring system.